Reference to Co-Pending Applications
Reference is hereby made to the following co-pending patent applications filed on even date herewith and assigned to the same assignee "TOP POLE PROFILE FOR POLE TIP TRIMMING" Ser. No. 07/480,250; and filed Feb. 15, 1990 "METHOD FOR TIPS IN A THIN FILM HEAD" Ser. No. 07/480,558, filed Feb. 15, 1990.
1. Field of the Invention
The present invention relates to production of thin film magnetic heads. In particular, the invention relates to aligning the upper and lower pole tips in a thin film magnetic head using a sacrificial mask layer in which only the gap material and bottom pole are milled.
2. Description of the Prior Art
Thin film magnetic read/write heads are used for magnetically reading and writing information upon a magnetic storage medium such as a magnetic disk or magnetic tape. It is highly desirable to provide a high density of information storage on the magnetic storage medium.
Increased storage density in a recording system may be achieved by providing an areal density as high as possible for a given recording surface. In the case of rotating disk drives (both floppy and hard disk), the areal density is found by multiplying the number of flux reversals per unit length along the track (linear density in units of flux reversals per inch) by the number of tracks available per unit length in the radial direction (track density in units of tracks per inch).
As track densities have approached and exceeded 2400 tracks per inch, the alignment between the upper and lower pole tips in thin film magnetic read/write heads has become critical. At such a high storage density, design criteria require magnetic transducers in which the bottom pole tip width is very nearly the same as the top pole tip width. Top and bottom poles should also be in close alignment.
A technique which provides better pole alignment begins with a top pole, bottom pole and a gap area separating the top and bottom poles, all fabricated substantially wider than desired A narrower mask layer is then deposited upon the upper pole. The structure is then aligned using a material removal process ("milling") such as ion milling or reactive ion milling in which high energy ions bombard the pole tip region to remove the excess material (top pole, bottom pole and gap material) that extends beyond the edges of the masking layer. The mask layer protects only a portion of the top pole, bottom pole and gap so that the width of the completed pole tips is approximately the same as the width of the mask layer.
The noted alignment technique is both slow and capital intensive. For example, assuming a top pole thickness of 4 microns, a bottom pole thickness of 3 microns and gap thickness of 0.5 microns, and further assuming the gap layer material has a milling rate about one-half the milling rate of the pole tip layers, the total shaping time is about 8 units of time. This is calculated with the formula: milling time=layer thickness.times.milling rate. For this example (4.times.1)+(3.times.1)+(0.5.times.2)=8 units of time.